UNM Computer Science

Operating Systems and Architecture
Comprehensive Exam
In-Class Version

August 19, 1997
Computer Science Department
University of New Mexico

All questions will count equally (about 15 points). Answer any seven of these 10 questions. Do not turn in answers to more than seven questions.

1. Log-structured file systems What is a log-structured file system? What file system problems is a log-structured file system intended to solve? How well does it solve them?

2. IPC Consider three methods of IPC (interprocess communication): shared memory, messages and RPC. Compare these three methods by giving the advantages and disadvantages of each one. Which can be implemented by using one of the others?

3. Access control lists Describe the access control list method for protection. Show how the UNIX protection system can be implemented with an access control list.

4. File caching In the Plan-9 operating system the local disk on a workstation contains no permanent files. The only permanent files are on the file servers on the network. The local disk contains swap areas and is a cache for files on the file server. Discuss the implications of this decision on the design of the operating system running on the local workstation.

5. Network file systems Describe how a network file system would be implemented. Assume you have an ordinary single machine operating system on the client machine and the file server machine. What changed have to be made in each operating system to support a network file system?

6. Inverted page tables What is an inverted page table? What problem is it intended to solve?

7. Hazards What are the four types of hazards encountered during instruction interpretation pipelining? Give a description of each hazard and an example using a load/store style instruction set. How do these hazards relate to data dependencies.

8. Caches Describe a simple snooping cache coherence protocol (either write-update or write-invalidate). When is a snooping protocol appropriate and when is it inappropriate?

9. Caches Give a brief description for each of the three types of cache misses. In addition, give a brief description of a technique that could be used to lessen the impact of this type of miss.

10. Instruction scheduling What is the goal of dynamic instruction scheduling? Why might you expect that dynamic scheduling would do better than static scheduling? Briefly, describe a technique that provides dynamic instruction scheduling.